Growth of beryl crystals



1966 A. A. BALLMAN ETAL 3,234,135

GROWTH OF BERYL CRYSTALS 5 Sheets-Sheet 1 Filed May 4, 1962 BALLMAN L/NARES JR.

A. A INVENTORS R. C.

o o O n By .l AN u/rE/er ATTORNEY 1966 A, A. BALLMAN ETAL 3,234,135

GROWTH OF BERYL CRYSTALS Filed May 4, 1962 3 Sheets-Sheet 2 ,4. ,4. BALL/WAN mum/709s R. C. L/NARES JR. L. a. VAN u/rERr ATTOR EV 1966 A. A. BALLMAN ETAL 3,

GROWTH OF BERYL CRYSTALS 3 Sheets-Sheet 5 Filed May 4, 1962 SOURCE OF PUMP/N6 POWER T N r SE N M R L U LM T A/A A r M ,b a mmw ARI. 8 S V. H M B w W M E w w ET VAM N n w mm 5 wfi mm III A 3 N 2 W3 NMU ML GOP PW PUMP/N6 POWER FROidZSC/LLA TOR United States Patent 3,234,135 GROWTH OF BERYL CRYSTALS Albert Ballman, Woodbridge, :NJ., Robert C. Linares, Jr., Framingham, Mass, and Le Grand G. Van Uitert, Morris Township, Morris County, N..I., assignors to Bell Telephone Laboratories, Incorporated, New York, N.Y., a corporation of New York Filed May 4, 1962, Ser. No. 192,409 16 Claims. (Cl. 252-625) This invention relates to the growth of single crystalline beryl (Be Al Si O by transfer crystallization out of a flux containing vanadium pentoxide. Crystals grown in this manner are of interest for electrical applications, as in microwave masers including those of the cavity or traveling wave type and as gem stones. In either use, any of the usual inclusions of interest may be added.

Recent developments in electrical circuit elements such as parametric amplifiers, transistors, and microwave and optical rnasers have stimulated concomitant developments in the crystal growing arts. Various techniques including flame fusion, spontaneous and seed nucleation, both from aqueous and non-aqueous flux, as well as hydrothermal procedures have in general resulted in the crystallization of materials suitable for these purposes. Crystalline ma terials which are now commercially synthesized include semi-conductor materials such as silicon, germanium, and the III-V intermetallic compounds, ferrimagnetic materials such -as yttrium-iron garnet and the various ferrites, and oxidic materials such as sapphire including various paramagnetic ions, calcium tungstate, and various molybdates, as well as a host of others. Many of these developments have resulted, too, in the growth of excellent gem stone crystals.

Despite this intense interest in such crystalline materials, however, there is at this time no generally accepted, commercially feasible system for synthesizing beryl. While recorded interest in the growth of beryl containing chromium goes back some seventy years (see P. Hautefuille, A. Perrey, 106 Comptes Rendus, 1800 (1888) and while subsequent literature references suggest the possibility of such synthesis by most of the techniques described above, no general solution has been disclosed. Impetus has recently been given to the search by the wide scale adoption of the microwave maser, particularly that of the traveling wave type (see United States Patent 3,004,235). While many such devices containing ruby elements are in use, it has been found that certain of the properties of beryl containing chromium suggest the substitution of this material at least for certain applications. For example, it has been determined that the latter material exhibits a higher zero field splitting, so permitting increased splitting for comparable magnetic fields and, thus, the attainment of higher operating frequencies, perhaps in the millimeter region. In the gem stone field, while most natural crystals are easily synthesized by commercially feasible methods, methods for the production of emeralds and other suitable green-colored gem stones have not been disclosed.

In accordance with this invention it has been determined'that beryl. crystals of a high degree of perfection with or without inclusions of interest from a microwave or gem stone standpoint are produced out of a flux containing vanadium pentoxide by a transfer technique. Preferred embodiments described herein include growth on selected faces so as to minimize occlusions, and the use of excess beryllium and aluminum oxides to prevent formation of a glassy face which otherwise may interfere with crystalline growth. Inclusion of chromium or iron in varying amounts may result in colored crystals known to the gem industry as aquamarine, emerald, and mor- Patented Feb. 8, 1966 ganite. Chromium and iron are illustrative of the trivalent paramagnetic ions which may be substituted for aluminum to produce desirable electrical properties.

Description of the invention is expedited by reference to the drawing, in which:

FIG. 1 is a perspective view of a natural hexagonal beryl crystal;

FIG. 2 is a cross-sectional view of apparatus suitable for the growth of beryl by a seed process in accordance with this invention;

FIG. 3A is a perspective view of a seeded growth produced on a slice cut normal to the cards;

FIG. 3B is a perspective view of a seeded growth produced on a slice cut to include the plane defined by the cand a-axis;

FIG. 4 is a cross-sectional view of apparatus being used for spontaneous nucleation by a transfer process herein;

FIG. 5 is a perspective view, partly in section, of a cavity-type microwave maser including a crystal of beryl grown in accordance with the instant invention; and

FIG. '6 is a perspective view, partly .in section, of a traveling wave type microwave maser, also containing a crystal grown in accordance with the processes herein.

Referring again to FIG. 1, there is depicted a crystal 1 of beryl which represents a typical growth habit. In this figure, the c-axis of the crystal is vertical, defining the major axis. The upper hexagonal face 2.34567 normal to the c-axis defines an a-plane. Gther natural faces, usually quadrangular in shape, illustrated by 67-89 occur parallel to the c-axis. Such natural faces may represent a plane defined by the cand a-axis or one defined by the c-axis and the direction perpendicular to an a-axis and a c-axis. In accordance with this invention, seeded growth is most advantageously carried out on one of the three natural faces discussed. In accordance with a preferred embodiment herein, it is shown that most perfect growth results from a seed including or parallel to a natural rectangular face. In discussing such crystal faces, it is to be understood that reference is bad to ideal crystallographic faces. Actual crystals from which seeds are cut may contain additional capping or other faces.

FIG. 2 depicts a furnace 15 and contained receptacle 16 in which seeded growth in accordance with this invention is being carried out. While any furnace capable of attaining a temperature of the order of 600 C. or any higher temperature specified herein is suitable for the practice of this invention, the high evaporation rate of molten flux material (V 0 1'7 and its high rate of reactivity with many materials such as the usual conductive materials results in a preference for a protective liner where a resistance type furnace is used. Apparatus found particularly suitable is that containing a high density alumina core. Alternatives include lnconel, Mullite, or other suitable lining materials. In the figure, sectional member 18 may be considered as representing across section taken through a toroidal core of such a furnace. Receptacle 16, shown as including seed crystal 19 suspended on hanger 20 and immersed in molten flux 21 and also containing solid nutrient material 22 is supported by block 23, which may be a refractory ceramic. While a vertical temperature gradient from bottom to top within the flux material 21 is required for the transfer processes herein, energy is conserved by use of a loosely fitting lid 24 made of zirconia, alumina, or other suitable material. It may be desirable to include a baiile 25 to confine nutrient material 22 and/ or to establish a desired temperature gradient.

FIGS. 3A and 3B illustrate two types of seeded growth which may result by use of the apparatus and process depicted in FIG. 2. Hexagonal growth, shown in FIG. 3A, results from immersion of a seed crystal 30 including 3. or parallel to a natural hexagonal face such as 2-'3-45- 6-7 of FIG. 1. It is seen that under these conditions growth is primarily in the c direction, the resulting product exhibiting the hexagonal faces typical of the natural habit depicted.

In FIG. 313, growth resulted from immersion of a seed including or parallel to either of the types ofi natural quadrangular faces discussed in conjunction with FIG. 1. While, for simplicity, growth is shown primarily in a direction normal to the major faces of seed 35, ;it.is to be recognized that a certain amountof c direction growth results so that the actual product manifests some 5 edge growth normal to the minor faces of the seed as Well as to the major faces. Such edge growth is at a maximum at the seed and is reduced in the direction of growth normal to the major seed faces.

FIGS. 3A and 3B are not to. be construed as restrictive, it being understood that growth results regard-. less of the orientation ofthe seed crystal.

FIG. 4 represents a receptacle containing nutrient 41 and flux 42, :as herein discussed, but in which growth is proceeding spontaneously so as to result in deposits 43.

and 44. Suitable apparatus for such a spontaneous process is identical to those considered in conjunction with the apparatus of FIG. 2, andreceptacle 40 may be treated. as being enclosed in the furnacethere depicted. Since no provision need be made for insertion of a'seed, cover lid 45-may be solid, as shown. Again,.the use of a bafile such as 46 may be advantageous as discussed in. conjunction with FIG. 2.

FIG. 5 depicts a cavity type microwave maser device such as that described in United States Patent 2,981,894. Utilizing the materials grown in accordance with the present invention, such devices, as well as the traveling type counterpart of FIG. 6.are capable of producing os- I cillation orv amplificationof microwave energy of wave lengths as high as those in the millimeter range by stimulated emission. While a more complete description of the device appears in the aforesaid patent specification, a brief description is set forth below.

Cavity maser device 50 depends. for its operation on: beryl crystal 51, which contains one or more paramagnetic:

ions as discussed herein. Crystal 51 is housed in a cavity resonator-52 which is desirably maintained at operating temperature by a suitable refrigerating apparatus shown schematically by the broken lines 52A. Pumping power of the appropriate frequency is supplied from a local oscillator 53 by way of a coupling loop 54. Input signal power is applied from source 55 by way of coupling loop 56.: It,

is advantageous to include an isolator 57 in the signal path. Output signal poweris abstracted from the'resonator by load 58 by way of coupling loop 59.. A second isolator 60 is shown along the signal path intermediate the load and cavity resonator. Pole pieces 61 are included to achieve the desired field splitting necessary to match the signal frequency.

A traveling wave solid state maser of the type-described is described in United States Patent 3,004,225.

At this time commercial interest in microwave maser devices is largely centered on the traveling wave device by which obtain in common with other slow wave devices.

In the figure there is shown a shorted section of a rec- '60 reason of the larger amplification and other advantages tangular waveguide so proportioned as to support a stand- 1 ing wave .of pumping power, fed from an'oscillator not shown, by a waveguide 71 through an iris 72 in one end of wall 73 of section 70. Mounted in a base member 74 and containedby the waveguide section 70 is a spaced parallel array of conductive elements 75 which are orthogonally disposed with respect to the longitudinal axis of the section 70. The elements 75, Whichare advantageously copper, plated tungsten rods, are secured to the base member 74. The end elements of the array 75 are, respectively, the terminal portions of the center conductors of two coaxial transmission lines 77 and 78, line 77 forming aninput path for a signalwave to the section.

70 and line 78 serving to abstract from the section or amplifying chamber 70 an amplified replica of the signal wave.

The device depends for its operation on 53. plurality of spaced blocks 80 of a negative temperature material,i which in this instance is composed of athesynthesized.

beryl containing one or more paramagnetic ions produced by the invention herein. Blocks 80 are separated by inter-- mediate, spacer blocks 81 of a material having a dielectric constant to match that of beryl. blocks 80. Suchspacer' blocks may becomposed of beryl, alsogrown by the process herein but'containing no paramagnetic ions. Posir,

tioned onthe other side (bottom side inFIG. 6) of-the array of elements 75' is a bar 82 which manifests a nonreciprocal gyromagnetic rotating effect due either to its own homogeneous properties or to the inclusion of isolator elements such'as83. While'in the latter case the gyromagnetic influence is produced 'by the ferrimagnetic rotation of a material such as yttrium-iron garnet, in theformer the influence may, result from the paramagnetic;

rotation effected at low temperature by use. of a bar 82 which, :again, may be composed-of a beryl crystal grown in'. accordance with the procedures herein. In accordance with such alternative embodiment, it is necessary to regulate the-paramagnetic ion inclusion or to misorient the. material of bar 82'relative to the orientation of blocks 80 I so as to cause bar 82 to act as a positive temperature absorber of reflected signal wave energy rather than as a negative temperature medium (range of from one to five percent is suitable).

The maser structure depends for its operation upon a static magnetic field indicated by arrow 86 parallel to the rods 75 and through the volumes, of the blocks 80 and 83 by means of which field both the zero splitting necessary for achieving the required discrete energy. levels in the materials of blocks '80 and also the nonreciprocalabsorption characteristics of the bar 82 are established.

It is convenient to describe the inventive processes ingeneral terms. This'discussion; presented in two parts, the first directed to seeded growth and the second to transfer spontaneousnucleation, is set forth with reference to the apparatus of'FIGS. 2 and 4,'respectively. Suitable parameter rangesare set forth. Following the general description, specific examples relating to growth 0f various types of beryl material are listed. Discussion is, for expediency, in' terms of V 0 flux although, as discussed, additional material may be present'in the flux.

GENERAL DESCRIPTION Into .a platinum or other suitable container, in this il-; lustration of a capacity of cc., are inserted reacted beryl, either. natural or synthesized,- or in the alternative, the components necessary to produce the:composition (e.g.,- BeO, A1 0 and SiO;,) To .thismay be added any paramagnetic ion or other ion inclusion desired, such ,for example as the chromium and/ or. iron commonly present in the natural-crystals. In the event the, components are inserted, the amounts are identical to or approximately,

those required for thedesired stoichiometry. In either event, excess beryllium or aluminum may be included-in other transfer processes, the amount of :the .fiux finally present is not critical, its: only purpose being to serve. as a To thistthere is added a total amount of'fluX.

transfer path from nutrient to growth position. Since, however, the V is a solvent for the nutrient, the maximum amount of such medium permissible is just short of that which results in total solution. In this illustrative example (four inch high crucible), the amount of V 0 eventually added isthat required to cover the seed crystal position (approximately 180 grams of V 0 Depending on whether the nutrient material is reacted beryl or the starting components, there is a difference in the, procedure by which theV O is added. In the former situation, it is necessary only to add the total amount of required transfer medium. In the latter, due to the evolution of gases, resulting from decomposition of the components, it is recommended that only that amount of V 0 necessary to result in a molten body covering the components be initially added, after which the temperature of the. contents of the receptacle, is raised so as to melt the transfer media and decompose the components, the temperature then being maintained at such level for a period necessary to decomposethe components and react so as to result in formation of the beryl'and oxides of any excess components included. After a suitable sintering period (of the order of several hours) following gaseous evolution, the remaining V 0 is added, the additional amount being such as to raise the level to above the position of the seed crystal.

It is next necessary to bring about thermal equilibrium between an inserted seed and the transfer medium. This is accomplished by inserting the seed crystal 19 into the molten V 0 and maintaining the two at temperature. Where this period is to be prolonged and it is desired to dissolve a portion of the surface layer, it may be necessary to use a somewhat thicker crystal. The inserted seed crystal faces will continue to dissolve until the transfer medium has become saturated with respect to beryl in the vicinity of the seed. Where dissolution is to be minimized, the container and contents are maintained at temperature for a prolonged period prior to-insertion ofthe seed. For the illustration discussed, it has been found that a period of several hours is required to produce saturation at the seed crystal position.

In either event, saturationmay be accelerated by stirring. A suitable operating temperature rangeis defined by expediency at the low end, it being found that reasonable growth rates are achieved only with temperatures of the order of 600 C. and higher. A maximum temperature limit is imposed by the tolerable rate of evaporation of the V 0 fiuxwhen operating in an open system. From this standpoint,.it is. recommended that temperatures of appreciably above. 1200 C. not be exceeded.

As discussed, nutrient materials may comprise fully reacted beryl, as from a natural orother source, which may or may not contain the paramagnetic ions or other inclusions desired. In addition, the nutrient may consist of any components which will react to yield the desired beryl composition. Illustrative component materials in addition to the elements themselves are beryllium compounds (oxide, nitrate, sulfate, silicate, chloride, et cetera), aluminum compounds (oxide, hydroxide, sulfate, aluminate, nitrate, et cetera), the silicon-containing material (silica, silicic acid, lithium silicate, silicon carbide, silicon oxide, et cetera'), together with any other ion-containing material desired. Such additional compounds may include those containing chromium, iron, manganese, et cetera. Amounts of such inclusions are determined by the desired end product, it being kept in mind that, only approximately one-half of such material included in the nutrient is eventually included in the growing crystal. Where it is desired to grow gem stone compositions, the amount of ion inclusion in the nutrient is as follows:

Aquamarineabout one-half of one atom percent of chromium based on the aluminum in the crystal (about one percent to be included in the nutrient).

Emerald-amounts ranging up to as high as five atom percent of chromium based on the aluminum inthe crystal (again of the order of two times this amount is required in the nutrient to result in such crystal composition).

Morganite-from a small fraction up to five atom percent of iron based on the aluminum in the crystal (same excess required, in the nutrient).

For microwave applications, where the material is to serve as a negative temperature medium, at least one paramagnetic ion is. included in the crystal. An exemplary inclusion is of the order of .5 atom percent, again based on the aluminum in the crystal. The most common paramagnetic ion added for this purpose is, again, chromium. Where it is desired to reduce relaxation time in the product crystal, it has been found that such desiderata may be achieved by the additional inclusion of iron, the order of this inclusion being up to about 3 percent, based on the aluminum in the crystal. Where the product crystal is to serve as a positive. temperature absorber rather than a negative temperature medium, larger amounts of paramagnetic ion are conventionally added. Such amounts may range from 3 to 10 atomic percent.

It has been mentioned that seeded growth is desirably carried out from a plane including or parallel to a natural crystal face. While growth may proceed from any orientation, the natural growth habit results in a more uniform product. Most rapid growth in beryl is in the c direction, such growth beingadvantageously produced from a natural hexagonal face or a seed cut parallel to such a face. While growth from a natural quadrangular face or a seed cut parallel to such face is slower, any occlusions are minimized and a more perfect crystal results. Typical growth rates are 30 to 50 mils per day in the c direction and 10 to. 30 mils per day from a quadrangular seed. For the illustrative process discussed herein, typical seed sections may be of dimensions of the order of mils, thick and of any major dimensions which may be accommodated by the receptacle- For this apparatus, crystals have been grown on seeds of the order of 2 inches square. Where the seed is to be inserted in the flux prior to the attainment of saturation at this position, it may be desirable to use thicker sections of the, order of perhaps mils or larger. In general, the nature of the nutrient, both as to the aggregate distribution and size, as well as purity, are not critical. It is, however, preferred that the nutrient materials have minimum particle dimensions of the order of 10 mils to permit sintering and to keep the rate of transfer within controllable bounds. Where it is desired to minimize the rate of growth at any particular operating temperature, this may be achieved by increasing particle or aggregate size or by the. use of baffies. Where the nutrient material is reacted beryl, it is preferred that particle or aggregate size be no smaller than about 10 mils, again to prevent unduly rapid transfer.

It has. been observed that the use of nutrient, whether reacted or components exactly equivalent to the stoichiometric requirements of the end product, results in the initial formation of a certain amount of glasseous material of a composition having a high silica content due to the high solubility of beryllium and aluminum. While such formation may be permissible, it is likely to inter fere with crystalline growth and may necessitate removal of the seed one or more times during the process. In accordance with the preferred embodiment herein, it, has been found that the use of excess. beryllium and/or aluminum may eliminate such formation. To this end it has been determined that glass formation is substantially avoided by saturating the solution with respect to both beryllium and aluminum. Exceeding this solubility limit is not harmful and results merely in the precipitation of beryllium and. aluminum compounds. It has been observed empirically that excess of both of the concerned elements of the order of one weight percent of the is sufficient to ensure uninterrupted crystalline.

growth;

The desirability of pretreating the nutrient beryl to,

remove occludedwater has been discussed. The same. reasoning dictates a similar pretreatment of the seed:

ture of the order of about 500 C, or higher and maintaining .it at such temperature for a period of several hours. 'Ithas been indicated that a temperature range.

of from 700 to 1200 C. is suitable for the operation of Y procedures herein... One .of the chief advantages, how ever, of the V flux is the fact that it exhibits a fairly. low viscosity and that it can be heated to relatively. high temperatures without appreciable dissociation, so per mitting a fairly rapid growthrate. Such considerations,

together with the desire to minimize loss of materials.

through evaporation, give rise to a preferred temperature range of from.800 to 1150" C. with optimum conditions being attainedat about 1050" C. All of the procedures covered herein are transfer processes. Consequently,

rate of growth is dependent. not solely on the average or. over-all temperature ,withinthe receptacle but also on the temperature diiferential between the position of ;the

nutrient and the position of the seed. In general,it has been found that a minimum differential of the order of 5 C. is required. The desire to maintain an orderly growth mechanism gives rise to a maximum temperature differential of theorder of 500 C. Of course, a smaller gradient is permissible where slower growth rates may be tolerated.

The general procedure has been described in terms of seeded growth. The spontaneous transfer procedure of 1 FIG. 4 is carried out in identical fashion except that a seed crystal is not inserted into the flux. All other considerations, including temperature ranges,-flux, and nutrient and concentrations, are identical. The spontaneous transfer procedure is facilitated ,by the fact that the beryl or nutrient components all have a specific density higher than-that of the molten flux at the optimum temperature .of 1050 C. or higher, so providing a natu ral separation between this material and the. growing crystals. Such separation at lower temperatures can be facilitated by the use of. baflles to hold the components down. Baffles may also reduce growth rateand limit the Since movement of particles .bythermal convection. spontaneous growth may result inhomogeneous crystals manifesting natural faces not dissimilar to those .illus-' trated by FIG. 1, it is this-type of growth which may be of-primary interest to those concerned with the synthesis of :gemstone quality material. While such crystals may be of interest for use in microwave devices, it has been, noted that the. controlled growthresulting from seeding,

on a rectangular plane coincident, with orflparalleLto a natural face is of high quality and is most desirable for such applications. 'In common with other spontaneous nucleation processes, the size and-quality of the resultant crystals: are strongly'dependent upon growth rate, slower rate favoring improvementin both parameters.

The following specific examples illustrate the growth of both seeded and spontaneously nucleated berylcontaining various inclusions by the inventiveprocesses. All runs were carried out in a 100 cc. crucible. All seedcrystals were pretreated at 500 C. so as to removewater prior to insertion in the flux.

Examplel.Seed growth of clear beryl without excess BeO OFA1203 30 grams of natural white beryl of an aggregate size of approximatelyone-quarter: are placed in the bot-.

tom of the crucible beneathfa baffle to which is added.

180 grams of.-'V' O The cruciblenand contents are heated ,to a temperature of approximately 1050 C. over a period of approximately twenty-four hours, after which the cover is removed, and a glassy material which had formed at the surface is removed. Two natural white.

beryl seed crystals of approximate dimensions 1 x 1". x 100-m1ls are immersed in the now molten flux, the depth of immersion being sufiicient to cover; .the .top of the.

crystal. The crucible and contentsiare maintained atthe said temperature for aboutfour days. One of the seeds has a hexagonal face; the other, a rectangular. endof-four da ys,-growth is observed on both fiat faces of said crystals. Growth on the firstseed (that including a hexagonal face) isiof the. order of 160 mils on each side; that on :the secondseedis of the order of 120 mils; also .on each side;.

20 Example 2.',-Gr0wth*ofchromium-doped beryl' from aflnx containing excess beryllium and1aIuminum' 4 The procedure of Example .1 is carried out,'substitut-. mg, however, thefollowing components and amounts for.

the white .beryl nutrient:

' Grams B lslz'i zQ r 23 Al(OH). V V 10- H' SiO 15.6- NHgcllsoioz 1 Sixty grams of vanadium pentoxide are inserted The crucible and icontents are raised to a :temperature of 1000 C. over a ;period:of approximately two hours and.

are maintained at this. temperature overnight to. permit the formation ofberyl and other; oxides. At the ,endof this period, 120 grams ofV O ,togethenwith one additional gram of NH Cr(SO are added, so bringing thelevel of :the fiux rnear. the'top of the crucible. Twoseed crystals, both of natural White beryl, both manifesting natural rectangular faces, and. both' of approximate dimensions 1" x 1 x 100 mils; are inserted. The cruglble and contents are maintained .at 1000 C. for four ays.

face .of both crystals;

The grown crystals contain of the; order of one atomic percent chromiumrby' weight of the aluminum.

Example 3.Gr0wt h of material of Example 2 with difliering starting components.

The procedure of Example. 2 is repeated howeversue stituting 3 grams ofberyllium oxide for: the-- .and..6 grams of -Al O for the Al(OHi) The operat-.

ing temperature-for this example .is. 1 100 'C. As .in

Example 2, glass formation is avoided by the use of ex-.

7 cess inclusions of :beryllium and/aluminum; After removal of theseeds at the termination of the four-day period, emerald growthof the orderv of: mils on each of the fourfaces is observed.

Example 4.-Seeded growth -0fmorganite The same type: and amounts of startingv components .are usedas in Example 2.i In lieu, however, of theinclusion of a. chromium-containing compound, there is added 0.3 gram of Fe(-NO Sixty grams of v Og are added. Crucible and contents are .raised to. a temper? ature of .950; C. over a period of two hours and the said temperature is; maintained overnight; of this. period, .120 grams of-V Q5, together-with an .ad

ditional 2 grams of Fe,(NO -6H O; are added; The

temperature of thecontents. is maintained at 950 C.;

again overnight, after which two rectangular: seed plates 1" x l"'x 100 mils are inserted. Seedand crucible con- At the:

Removal of .the seeds discloses an emerald-green; growth of. a thicknessofaapproximately m mils'on each Visualv examination and microwave measurements. disclose the, material to be emerald;

At the end tents are maintained at a temperature of 950 C. for one week. 75-mil growth of morganite is observed on each of the major exposed faces.

Example 5 .-Seeded growth of beryl containing chromium and iron The initial components are as follows:

Grams Be(NO3)2' Al(OH) 8 H SiO 15 .6 F(NO3)36H20 NH Cr.(SO .15

To these starting components there is added 60 grams V Crucible and contents are raised to a temperature of approximately 1000 C. over a period of approximately two hours. Contents are maintained at this temperature overnight, after which 120 grams of V 0 an additional 1.25 grams of the iron-containing compound, and .15 gram of the chromium-containing compound are added. The entirety is again maintained at a temperature of 1000" C. overnight so as to bring the flux to saturation, after which two rectangular seed plates of natural white beryl of approximate dimensions 1" x 1" x 100 mils are inserted. Crucible and contents are maintained at 1000 C. for a period of approximately seven days. Resultant growth is approximately 145 mil thick on each of the four exposed faces.

Example 6.Growth of beryl containing small amount of chromium The starting components are:

Sixty grams of V 0 are added and the receptacle and contents raised to a temperature of 1000 C. in a period of two hours and maintained at this temperature overnight. At the end of this period, an additional 120 grams of V 0 together with 0.3 gram of Nl-l Cr(SO is added. Contents are raised to a temperature of 1000 C. and again maintained at that temperature overnight. Natural white beryl slices of approximate dimensions 1" X 1 x 100 mils are inserted, the temperature is raised to 1000 C., and the contents are maintained at such temperature for a period of one week. The resultant growth reaches a thickness of approximately 150 mils on each of the four faces. The material is aquamarine in color. Microwave measurements show a line width "of approximat ly 100 me.

Example '7.--B-eryl and chromium growth by spontaneous nucleation The procedure of Example 1 is carried out, substituting however the following components and. amounts for the white beryl nutrient:

Grams Be(NO 3H O 23 Al(OH) H SiO 15.6 NH4CI'(SO2) 2 1 Sixty grams of vanadium pentoxide are inserted. The crucible and contents are raised to a temperature of 1000" C. over a period of approximately two hours and are maintained at this temperature overnight to permit the formation of beryl and other oxides. At the end of this period 120 grams of V 0 together with one additional gram of NH C1'(SO are added, so bringing the level of the flux near the top of the crucible. The crucible and contents are maintained at 900 C. for two months. At the end of this period the cover is removed. It is observed that natural emerald crystals have formed at the liquid line, such crystals being of dimensions of 10 up to one carat in size. The grown crystals contain of the order of one atomic percent chromium by weight of the aluminum.

Example 8.Seed growth of chnomium-a'oped beryl from V 0 additionally containing 7% U0 30 grams of natural white beryl of an aggregate size of approximately 4 inch is placed at the bottom of a crucible beneath a baffle having apertures a little smaller than /4 each to which is added grams of V 0 7.4 grams of lithium carbonate (representing about 7 percent by weight lithium oxide based on total flux), 0.2 gram of Cr O together with 5 grams excess A1 0 The crucible and contents are heated to a temperature of approximately 700 C. over a period of approximately five hours. A beryl seed crystal of approximate dimensions A x /2" x 100 mils is immersed in the molten fiux, the depth of immersion being sufficient to cover the top of the crystal. The seed is cut parallel to an a face. The inserted seed is rotated during the entire crystallizing process at a rate of approximately 80 r.p.m. The crucible and contents are maintained at the said average temperature for a period of about four days. During this period a gradient ranging from approximately 930 C. in the vicinity of the nutrient down to a low of about 880 C. at the position of the seed crystal is measured. At the end of four days, growth is observed on both fiat faces of the crystal. A total growth of about mils (about 60 mils on each face) results.

, Example 9.-Seed growth of chromium-doped beryl from V 0 additionally containing 15 LiO Example 8 is rerun under identical conditions except that the lithium content is increased to about 15 percent (14.8 grams lithium carbonate) together with the same amount of V 0 The growth at the termination of the four-day period is approximately the same as that observed in the preceding example.

It is noted from the examples above that widely varying amounts of excess beryllium and/or aluminum are adequate in ensuring the absence of glassy growth. In certain of the examples where paramagnetic ions were included, such inclusions were made in two parts, one Part being made initially and one part together with the final quantity of flux material. Where such inclusions are to be made, this procedure is considered to be preferred since it ensures replenishment of such ion during crystal growth, so resulting in more uniform doping. For expediency, the invention has been described in terms of a limited number of specific embodiments. Such embodiments were selected so as to differ one from the other in simple fashion. Many variations are possible and may be preferred. It is to be understood, for example, that the amount of V 0 is not critical, it being required only that there be sufficient flux to provide a liquid path from nutrient to seed position or, in the alternative, from nutrient to a position of sufficiently reduced temperature to result in spontaneous nucleation, and that the amount of flux be insufiicient to result in excessive solution of nutrient material. Where growth on but a single face of the seed is desired the path need include only such face. For seeded growth, the dimensions of the seed plate are limited largely by the size of the container. The apparatus utilized in many of the specific examples was conveniently operated with two seed crystals. Growth proceeds at substantially identical rates on a greater number of immersed seeds providing they are spaced at reasonable intervals.

The apparatus utilized in many of the examples was such as to result in a temperature gradient of the order of approximately 40 C. Smaller gradients are operative, however, resulting in a reduction in growth rate. Higher gradients may be tolerated. The absolute maximum imposed is set by the permissible maximum and minimum temperatures set forth above. It is feasible to operate with a gradient of 500 C. from hot temperature of 1200 C. to a cold temperature of 700 C. However, establishment of such a gradient would necessitate the.

use of a considerably deeper container than that discussed. It'is evident that the growth process proceeds generally without regard to intentional or unintentional inclusions. I

For certain of the purposes herein it is desirable to include critical factor, flux variations -may be .made ,generally without regard to the efiect on solubility. In fact, one purpose for varying the flux composition from pure V is to deliberately reduce solubility so as to decrease the rate of crystallization.

Inclusions of such materials made primarily to alter the solubility of the flux and so to vary the rate of crystallization may be made in amounts exceeding such limit.

While, as discussed in the preceding paragraph, broad deviations from pure V 0 flux may be made with impunity where the added materials contain ions of such valence or dimensions as not to appear in the final crystals,

For example, it has been found it is considered that additions of trivalent ions other than, A1 of nature such as to appear in the final composition;

should be made in amounts such as to result in a maximum inclusion of the crystals of the order of five percent by;

weight based on the entire crystal composition.

Variations in the growth procedures are evident. For example, it was noted in Example 1 that it was feasible to use a bafile to help fix the position and differential of temperature gradient, much in the manner that such an element is utilized in a hydrothermal growth procedure. All examples were carried out in air at atmospheric pressure. Other oxygen-containing atmospheres may be substituted. Increasing pressure, while probably not feasible from a commercial standpoint, excellent results being obtainable without the need for additional equipment, results in increasing solubility and, consequently, increasing rate of crystallization.

What is claimed is:

1. Process for the. crystallizing of a material consistingessentially of Be Al Si O by a transfer mechanism in a molten flux consisting essentially of V 0 comprising heating the said flux together with a solid nutrient selected from the group consisting of Be Al Si O and.

reactants capable of yielding Be Al Si O so as to produce a temperature gradient of at least 5 C. from a; minimum value of 700 C., the position of crystallization beingkeptat said minimum value and the position of the solid nutrient being kept at a temperature at least.

5 C. higher than the said minimum.

2. Process of claim 1 in which crystallizing is caused. to proceed on an immersed surface of an inserted seed.

of single crystalline material comprising Be Al Si -O 3.1 Process of claim 1 in which the said nutrient com-r prises Be Al Si O 4. Process of claim 1 in which the said nutrientcornprises, component materials which react to yield crystal-i.

line material consisting essentially of Be Al Si O 5. Process of claim 1 in which the said nutrient =ineludes an excess of at least oneelement selected from the groupconsisting of beryllium andaluminum with reference to the amount of said elementrequired to produce the stoichiornetry of-Be' Al Si O Y r 6. Process of claims-in which the-said element is,

chemically combined. a

7.1 Process of claim'5 in which an excess of both of:

said elements is included in the. nutrient.

8. Process of claim 1 :in which the said flux is at leastpercent .by weight -V' O 9. Process of .claim 8 in which the said flux contains.

up to 20 weightrpercentiof lithiumpxide.

10." Process of claim 1 in which the composition ofsaid nutrient is such as to yield a crystalline :materialcontaining at least, one additional trivalent ion in a maximum amount of 5 percent by weight based on .the said crystal line material.

11. Process of claim'9 in'which the said trivalention is selected from the groupgconsisting; of chromium. and

next.

12. Process of claim 11 @in' which the. composition of the nutrient is such as to result in a crystal containing both trivalent chromium and trivalentiron, thetotal amount of such inclusions being a maximumofS 'percent'based on the weight of the said crystalline material.

13. Process of claim 1 in :which the crystallizing is.

caused to proceed 2011 an immersed {seed comprising Be Al Si 0 the said seed having at leastonemajor face approximately parallelto .a natural quadrangular face of a crystal exhibiting a hexagonal habit. 14. Process of claim'13 in which the :said major face correspondsto said naturaliquadrangular face.

15. Process ofclaim 1 in :which the crystallizing is caused to proceed on :an immersed :seedcomprising Be Al Si O the said seed having at least one major face approximately normal to a.c-axis of a crystal exhibiting i a natural hexagonal habit.

16.: Process in accordance ,withclaim 1 iinwhich the crystallizing is caused to proceed on asurface of an im-- mersedseed comprising Be Al Si O inrwhich the said seed is heatedto a temperature of at least 500'' C; prior to immersion.

References, Cited by the Examiner UNITED STATES "PATENTS 1,579,033' 3/1926 Riera 42 3,003,112 10/1961 Van Uitert 25262.5

OTHER REFERENCES Dvir et al.: Paramagnetic Resonance and OpticalaSpe-; 'trum of Iron in Beryl, Chemical uary 1961, p. 1202.

'Hauterfeville ;et al.: 1888,: vol. 106, pp. 1800-1803.

TOBIAS ELLEVOW; Primary Examiner. MAURICE ..BRIND ,fiEzc m n n-, '1 I Abstracts, vol;- 55j Jan- Comptes Rendus, January-June; 

1. PROCESS FOR THE CRYSTALLIZING OF A MATERIAL CONSISTING ESSENTIALLY OF BE3AL2SI6O18 BY A TRANSFER MECHANISM IN A MOLTEN FLUX CONSISTING ESSENTIALLY OF V2O5, COMPRISING HEATING THE SAID FLUX TOGETHER WITH A SOLID NUTRIENT SELECTED FROM THE GROUP CONSISTING OF BE3AL2SI6O18 AND REACTANTS CAPABLE OF YIELDING BE3AL2SI6O18 SO AS TO PRODUCE A TEMPERATURE GRADIENT OF AT LEAST 5*C. FROM A MINIMUM VALUE OF 700*C., THE POSITION OF CRYSTALLIZATION BEING KEPT AT SAID MINIMUM VALUE AND THE POSITION OF THE SOLID NUTRIENT BEING KEPT AT A TEMPERATURE AT LEAST 5*C. HIGHER THAN THE SAID MINIMUM. 